Climate Change and the Rocky Mountains - Impact of Global Changes on Mountains: Responses and Adaptation - page 436

like the pygmy poppy ( Papaver pygmaeum ), a threatened endemic in the
Rocky Mountains of northwestern Montana and southwestern Alberta, are
distributed near and below snowfi elds and are dependent on snowmelt in
late summer for adequate moisture. Because the soil water holding capacity
is low at these elevations, the continued loss of snow and ice is expected
to severely reduce the abundance of the pygmy poppy. Lesica (2012)
reported loss of snow deposits, drying of tundra and local declines of half
the alpine species he monitored. Similarly, studies of snowbed vegetation
(i.e., vegetation that grows later in the season as pockets of late-lying
snowmelt) in Colorado and elsewhere suggest comparable dependencies
of alpine fl ora on persistent snow both for moisture and nutrients. Logan
Pass, in Montana, has a suspended wetland in the alpine zone that is fed by
meltwater from surrounding ice and snowfi elds and contains a rich fl ora
(Lesica 2002) that includes species on the edge of their ranges. This unique
biodiversity hotspot has been monitored for climate change impacts since
1988. Lescia and McCune (2004) found losses and reductions in abundance
consistent with a warming trend and earlier snowmelt. To date, there has
been no monitoring or estimates of change in the water balance for Logan
Pass but diminished snowpack is likely to affect the numerous springs that
allow this concentration of plants to persist.
Snowpacks accumulate atmospherically deposited nitrogen during the
cold season for as much as nine months and then slowly release nitrogen and
other nutrients with snowmelt during the growing season (Bowman and
Seistadt 2001). These nutrient inputs have large impacts on plant growth and
dynamics in the mostly inorganic environment in which alpine fl ora exist.
This fertilization effect may diminish in the future with the reduced presence
of snow in early summer when plant uptake peaks. However, Baron et
al. (2009) have documented additional nitrogen release from retreating
glaciers and rock glaciers as sediments are exposed during warmer and
drier summers. In some mountain areas atmospheric nitrogen deposition
has increased enough to become a problem for aquatic systems, so there
may be a compensatory effect if summer rainfall can deliver sporadically
what used to be provided continuously by melting snowfi elds. These
interacting effects of nitrogen deposition and changing climate are spatially
and temporally variable but are important to document for projecting how
alpine tundra vegetation will fare in the future.
Alpine vegetation on mountain summits is also likely to be susceptible
to warming air temperatures and diminished snow. Diaz and Eischeid
(2007) showed that the climate envelope that is unique to alpine tundra
has decreased in area by 73% in two decades and is likely to disappear
in the western U.S. in the near future. Plants in alpine tundra may fi nd
refugia by dispersing to other mountain aspects or thermally sheltered
microtopographic features (Scherrer and Korner 2011). But summit species,